Abstract

Soybeans [Glycine max (L.) Merr.] have undesirable levels of polyunsaturated fatty acids in their oil that result in oxidative instability and poor flavor. The process of hydrogenation improves the stability but creates undesirable trans fats. Lines carrying fan genes have decreased linolenic acid (18:3) content. Changes in transcription or activity of the desaturase encoded by the GmFAD3 gene cause a reduction in 18:3 content in certain lines. The objectives of this study were to determine the molecular basis of the fan allele in PI 123440, develop molecular markers to assay for the GmFAD3 gene in lines carrying fan(PI 123440), and estimate the variation in the 18:3 explained by the GmFAD3A locus. Sequence analysis of the GmFAD3A from ‘Soyola’, the fan(PI 123440) allele, and ‘Dare’ showed no sequence polymorphisms that would alter the amino acid sequence of the enzyme. RNA blot analysis of a low-18:3 line carrying a fan(PI 123440) allele, a line with normal 18:3 content, and three of their progenies showed a decrease in steady-state FAD3A RNA levels in low-18:3 lines. A marker for GmFAD3A was tested in two populations segregating for fan(PI 123440). Lines homozygous the GmFAD3A allele inherited from PI 123440 had a significant reduction in 18:3 when compared to lines homozygous for the GmFAD3A allele from the normal 18:3 parent. The differences between the two groups explained more than 77.5% of the genetic variation in 18:3 seed-oil content in the populations. In summary, a reduction in the steady-state mRNA levels of the GmFAD3A leads to a reduction in 18:3 synthesis within the developing seed in plants containing the fan(PI 123440) allele.

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